JP2001142432A - Display element driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformalize the display brightness of a dot matrix type organic EL display panel. SOLUTION: A drive voltage outputted from a variable constant voltage power circuit 11 is controlled so as to be proportional to distances up to one end part of transparent lines from intersectional parts of opaque electrode lines and the transparent electrode lines sequentially turned on in a time division manner in synchronism with each duty timing of an organic EL display panel. It is possible to offset a voltage drop caused by the internal wiring resistance of the transparent electrode lines, and stabilize voltage to be applied to each display dot.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arrangement in which a transparent electrode line and a non-transparent electrode line are arranged so as to intersect with each other. The present invention relates to a display element driving device that selects a transparent electrode line and applies a voltage to each display dot to perform duty driving of an organic EL display panel.

[0002]

2. Description of the Related Art A general organic EL display panel 1 is shown in FIG.
A plurality of linear anode lines (transparent electrode lines) 2 (1) to 2 (2) using a transparent electrode such as indium tin oxide (ITO) on a transparent substrate such as a glass substrate. m) are formed in parallel, an organic layer is formed on the back side of the anode lines 2 (1) to 2 (m), and a plurality of parallel layers are formed on the back side of the organic layer using an all-metal-deposited film such as aluminum. Cathode line (non-transparent electrode line) 3 (1)
To 3 (n) are formed so as to intersect the anode lines 2 (1) to 2 (m) at right angles, and one of the anode lines 2 (1) to 2 (m) is connected to the column driver 4 And apply a voltage, and select one of the cathode lines 3 (1) to
3 (n) is selected by the row driver 5 and grounded, so that the selected anode lines 2 (1) to 2 (m) and the cathode line 3 (n) are selected.
A current flows through the organic layer at the position where (1) to 3 (n) intersect to excite the organic molecules inside, and light is emitted when this transitions to the ground state. Thereby, the anode lines 2 (1) to 2 (m) and the cathode lines 3 (1) to 3 (m)
Intersection of (n) (hatched portion in FIG. 6)
Are lit and displayed as display dots (EL display elements). Note that, when viewed as a whole display element driving device, these dots are connected in parallel between the driving voltage Vout and the ground, and a parallel circuit is formed here.

Here, the column driver 4 is composed of a plurality of switching elements SA1 to SAm connected to the anode lines 2 (1) to 2 (m) of the organic EL display panel 1, and a control unit (not shown). When any one of the switching elements SA1 to SAm is switched on by the switching control in the above, the switching element SA which is turned on
Anode lines 2 (1) to 2 connected to SAm
A drive voltage is applied to (m) to drive a drive current I.

The row driver 5 is composed of a plurality of switching elements SK1 to SKn connected to the respective cathode lines 3 (1) to 3 (n) of the organic EL display panel 1. When any one of the switching elements SK1 to SKn is switched on by the switching control of
To the cathode lines 3 (1) to 3 (n) connected to SKn
Are grounded, and the drive current I flows.

In such an organic EL display panel 1, the switching elements SK1 to SKn of the row driver 5 are turned on in a time-division manner, and the switching elements S1 of the column driver 4 are turned on.
A1 to SAm are selectively turned on / off according to the display content while synchronizing with each divided time, so that when viewed visually, it is possible to perform a duty drive in which dots (pixels) appear to be turned on / off at the same time. Do.

[0006]

The organic EL shown in FIG.
In the display panel 1, the driving current I, which is a direct current supplied from a power supply, is applied to each switching element SA
1 to SAm, the switching element S turned on.
A1 to SAm, which flow through the anode lines 2 (1) to 2 (m) made of ITO to reach the organic layer which is a display dot, and further flow through the cathode lines 3 (1) to 3 (n) to ground. To the potential.

At this time, each of the cathode lines 3 (1) to 3 (3)
In (n), since each of the cathode lines 3 (1) to 3 (n) is formed of a vapor-deposited film such as aluminum, the wiring resistance is not so large. ) To 3 (n) need not be considered.

On the other hand, anode lines 2 (1) to 2
(M) is composed of ITO and therefore has a high resistivity. Therefore, the voltage drop from each of the switching elements SA1 to SAm to the organic layer as each display dot is not negligible compared to the drive voltage of the organic layer itself. become. And
The position of the organic layer as the display dot becomes farther in order at every vertical arrangement interval (hereinafter referred to as “duty section”) of the display dot in FIG. 6, so that the uppermost row of one frame of the organic EL display panel 1 is displayed. In the bottom row, the voltage drop due to the wiring of the anode lines 2 (1) to 2 (m) made of ITO is significantly different before reaching each display dot (organic layer).

As a result, the anode line 2 made of ITO
As the voltage drop in (1) to (m) increases, the driving voltage of each display dot (organic layer) itself decreases. That is, in the conventional organic EL display panel 1 shown in FIG. 6, the light emission luminance decreases as the screen goes down, and a luminance difference occurs between the upper and lower ends of the organic EL display panel 1, resulting in a remarkable display quality. Had been impaired.

An object of the present invention is to improve the display quality by making the light emission luminance uniform over the entire screen by applying a voltage in consideration of the voltage drop caused by the internal wiring resistance of the anode line made of ITO. It is an object of the present invention to provide a display element driving device which can be obtained.

[0011]

Means for Solving the Problems In order to solve the above problems,
The invention according to claim 1, wherein the plurality of thin-film-formed transparent electrode lines are arranged in parallel, and the plurality of non-transparent electrode lines are arranged in parallel so as to intersect each of the transparent electrode lines. And a non-transparent electrode line. A display element driving device that performs duty driving for an organic EL display panel having a dot matrix structure in which intersections between the non-transparent electrode lines and the non-transparent electrode lines are arranged in a matrix form. The switching elements are turned on in a time-division manner to sequentially switch the non-transparent electrode lines, and each switching element of a predetermined transparent electrode driver is selected according to the display content in synchronization with the switching of each switching element of the non-transparent electrode driver. Switch on / off to select the transparent electrode line, and apply a voltage to each display dot. In a display element driving device that performs duty driving of an EL display panel, the transparent electrode driver is connected to one end of the transparent electrode line, and applies a driving voltage to each of the display dots through the transparent electrode driver and the transparent electrode line. A variable constant voltage power supply circuit for switching on and off the switching elements of the non-transparent electrode driver in a time-division manner and sequentially switching the non-transparent electrode lines, in synchronization with the switching of each switching element of the non-transparent electrode driver. The switching elements of a predetermined transparent electrode driver are selectively turned on / off according to display contents to select the transparent electrode line, and the non-transparent electrode line and the transparent electrode which are sequentially turned on in a time-division manner. The drive in proportion to the separation distance from the intersection with the line to the one end of the transparent electrode line In which a control unit for controlling the variable constant-voltage power supply circuit so as to vary the pressure.

[0012] The invention according to claim 2 further comprises a current detection circuit for measuring a drive current output from the variable constant voltage power supply circuit, wherein the control unit is configured to detect a driving current based on a current detection result of the current detection circuit. The variable constant voltage power supply circuit is controlled so that the drive current is constant.

[0013] The invention according to claim 3 further comprises a temperature detecting element for detecting a temperature of the organic EL display panel,
The control unit is configured to determine an initial level of the drive voltage based on a result of temperature detection by the temperature detection element when application of the drive voltage to the organic EL display panel is started.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment <Configuration> FIG. 1 is a block diagram showing a display element driving device according to one embodiment of the present invention. In FIG. 1, components having the same functions as those of the conventional example shown in FIG. 6 are denoted by the same reference numerals.

In the display element driving device, in the duty driving of the dot matrix type organic EL display panel 1 by the constant voltage power supply, the output from the variable constant voltage power supply circuit (stabilized voltage supply circuit) is synchronized with the timing of each duty. The driving voltage Vout is controlled so as to cancel the voltage drop due to the internal wiring resistance of the anode lines (transparent electrode lines) 2 (1) to 2 (n) made of ITO, so that the organic layer as the display dot is controlled. In order to eliminate the luminance difference of the screen which has been a problem in the past.

Specifically, this display element driving device is shown in FIG.
Drives the dot matrix type organic EL display panel 1 of n rows × m columns as shown in FIG.
A column driver (transparent electrode driver) 4 for selecting a column of the L display panel 1, a row driver (non-transparent electrode driver) 5 for selecting a row of the organic EL display panel 1, and a variable supply of driving power through the column driver 4. Constant voltage power supply circuit (stabilized voltage supply circuit) 11, column driver 4 and row driver 5
Switching elements SA1 to SAm, SK1 to SKn
And an output voltage Vo output from the variable constant voltage power supply circuit 11 to the column driver 4.
and a control unit (display controller) 12 for controlling ut.

Here, the respective internal configurations of the organic EL display panel 1, the column driver 4 and the row driver 5 are the same as those of the conventional example shown in FIG.

The variable constant voltage power supply circuit 11 uses one NPN transistor as shown in FIG. 2, and uses the voltage from the battery power supply (+ B) based on the base potential given from the control unit 12. Vin is converted into a stabilized voltage Vout as an emitter potential.
In FIG. 2, for the sake of simplicity, the variable constant voltage power supply circuit 1
Although only one NPN transistor is shown as 1, the voltage Vin from the battery power supply (+ B) is actually used by using a voltage follower circuit (not shown) of the output voltage Vout.
It is desirable to make adjustments to offset the fluctuations when the fluctuations are large.

The control unit 12 includes a ROM, a RAM, and an MPU.
The microcomputer chip with built-in is used,
A software program stored in advance in a ROM
A functional component that is loaded into the AM and operates according to this software program, and supplies a voltage control signal as an analog signal through a built-in D (digital) / A (analog) conversion circuit (not shown) to the variable constant voltage power supply circuit 11.
Output. The control unit 12 supplies a column switching signal to the column driver 4 to switch the switching element SA1
To ON and OFF, and a row switching signal is supplied to the row driver 5 to switch on and off the switching elements SK1 to SKn. A voltage control signal is supplied to the variable constant voltage power supply circuit 11. Drive voltage V
out can be adjusted. This control unit 12
Is the operation itself of the entire display element driving device described later. In particular, as described later, the switching elements SA1 to SAm and SK1 to SK1 of the column driver 4 and the row driver 5 are used.
In synchronization with the switching operation of Kn (see FIG. 6), a voltage control signal to the variable constant voltage power supply circuit 11 is connected to the anode lines 2 (1) to 2 (m) of the organic EL display panel 1 (see FIG. 6). It is adjusted appropriately according to the resistance difference.

<Operation> FIG. 3 shows the switching elements SA1 to SAm, SK1 to SK1 of the column driver 4 and the row driver 5.
SKn ON / OFF switching timing and drive voltage Vout
4 is a timing chart showing the relationship with the above. In addition, the code | symbol T1 in FIG. 3 has shown the period when the control part 12 switches ON each switching element SK1-SKn of the row driver 5 all at once.

As shown in FIGS. 3 (2) to 3 (n), the control unit 12 controls each of the switching elements SK1 to SK1 of the row driver 5.
SKn is sequentially switched on in a time-division manner. In synchronization with this, the switching elements SK1 to SK of the row driver 5 are synchronized.
A display dot (organic layer) to be illuminated for each row selected by Kn is selected according to the display content, and the column driver 4 is selected.
Are turned on / off (see FIG. 6). This allows the viewer to see the organic EL
When the display panel 1 is visually observed, it appears that the display dots (pixels) as the organic layer are turned on / off at the same time.

Here, the control section 12 increases the voltage control signal (base potential) applied to the variable constant voltage power supply circuit 11 stepwise in synchronization with the switching operation of the switching elements SK1 to SKn of the row driver 5. Then, the drive voltage Vout output from the variable constant voltage power supply circuit 11 becomes
According to the change of the base potential given from the control unit 12,
As shown in FIG. 3 (o), the voltage increases stepwise in synchronization with the switching operation of the switching elements SK1 to SKn of the row driver 5.

Now, as shown in FIG. 4, an anode line (transparent electrode line) 2 and a cathode line (non-transparent electrode line) 3
, The length of the anode line 2 made of ITO in the line direction is L, and the width of the anode line 2 is W. The wiring pitch (duty interval) of the cathode lines 3 is P. And, for example, W = 1.00
[Mm], P = 1.0 [mm], and L is close to P. Further, the sheet resistance of ITO is, for example, 10
[Ω / □], and the number n of the cathode lines 3 is 64
[Individual].

In this case, the total length of the anode line 2 is 64 ×
1.0 [mm] = 64 [mm]. Therefore, the resistance from one end to the other end of one anode line 2 is
64 [pieces] × P / W × 10 [Ω / □] = 64 [pieces] × 1.0 [mm] /1.0 [mm] × 10 [Ω / □] = 640 [Ω]… ( 1)

On the other hand, for example, an organic EL display element emitting green light
The average number of children is 200 to 300 [cd / m ^Two] To emit light
In this case, 4 [mA / cm^Two]
What is necessary is just to flow an electric current with a flow density. However, here,
Example of switching the cathode line 3 one after another with Iva5
For example, if the number of cathode lines 3 is 64, 1
When the current is applied to the display dots 15 fully,
Is limited to 1/64. Therefore, 4 [mA /
cm^TwoThe light emission luminance is obtained only by passing a current at a current density of
Is reduced to approximately 1/64. Take this into account
And the row driver 5 cuts 64 cathode lines 3 one after another.
When replacing, the peak current flowing through each anode line 2 must be
By setting it to 64 times, the emission of each display dot 15
The brightness can be set appropriately. In this case, ITO
Current flowing through the anode line 2 per line consisting of
Is 1.0 × 1.0 × 10^-2[Cm^Two] X 4 [mA / cm^Two] × 64 = 2.56 [mA] (2) From equations (1) and (2), the anode driver
2 and the opposite end (reference numerals A and
No. B) is due to the voltage drop due to the wiring resistance of ITO.
640 [Ω] × 2.56 [mA] = 1.64 [V] (3) Therefore, for each section, in the step of 1.64 [V] / 64 [pieces] = 0.026 [V] (4), as shown in FIG.
If the drive voltage Vout from the power supply circuit 11 is increased,
In any duty section, one display dot 15
Can be made constant.

As described above, in synchronization with the timing of each duty of the dot matrix type organic EL display panel 1, the drive voltage Vout output from the variable constant voltage power supply circuit 11 is changed to the anode line 2 (1) made of ITO. ) ~
Since the voltage drop due to the internal wiring resistance of 2 (n) is controlled to be offset, the applied voltage applied to the organic layer as the display dot 15 can be kept constant, and thereby, each line of the organic EL display panel 1 can be controlled. The display brightness can be kept constant.

Note that the present invention is not limited to the configuration of the above embodiment, and various additional circuits may be added.

For example, as shown in FIG. 5, the drive current I outputted from the variable constant voltage power supply circuit 11 to the organic EL display panel 1 is periodically monitored by the current detection circuit 17, and the current is detected by the current detection circuit 17. Based on the result, this drive current I
May be controlled by the control unit 12 so as to adjust the drive voltage Vout. By doing so, not only the voltage control for offsetting the voltage drop due to the internal wiring resistance of the anode line 2 but also the adjustment of the drive current due to, for example, the aging deterioration of the organic EL display element itself due to the temperature change can be performed. The display luminance can be stabilized. As the current detection circuit 17, for example, a current mirror circuit or the like may be used.

As shown in FIG. 5, for example, by adding a temperature detecting element (thermistor) 18, the driving voltage Vout at the start of the duty driving is calculated and set from the temperature data detected by the temperature detecting element 18. It becomes possible. In this case, the current flowing through the organic EL display element can be calculated in advance and given, regardless of the temperature environment when the organic EL display panel 1 is started. Therefore, an excessive current does not flow, and the possibility of damaging the element is reduced. Also, in this case,
There is also an advantage that the drive voltage can be adjusted using temperature data instead of the drive current without providing the current detection function.

[0030]

According to the first aspect of the present invention, the non-transparent electrode line and the transparent electrode line that are sequentially turned on in a time division manner in synchronization with the timing of each duty of the dot matrix type organic EL display panel. The drive voltage output from the variable constant voltage power supply circuit is controlled so as to be proportional to the distance from the intersection with the transparent electrode line to one end of the transparent electrode line, so the voltage drop due to the internal wiring resistance of the transparent electrode line is driven. The offset can be offset by the increase in the voltage, and the applied voltage applied to each display dot can be kept constant, whereby the display luminance of each line of the organic EL display panel can be kept constant.

According to the second aspect of the invention, the variable constant voltage power supply circuit is controlled based on the current detection result of the current detection circuit so that the driving current is constant. It is possible to correct and adjust the change in the drive current due to the aging of the display element itself, and the display luminance can be further stabilized.

According to the third aspect of the present invention, an organic EL
When the application of the drive voltage to the display panel is started, the initial level of the drive voltage is determined based on the result of temperature detection by the temperature detection element. In this case, an appropriate level of the current flowing through the organic EL display element can be calculated in advance and given. Therefore, an excessive current does not flow, and the possibility of damaging the element is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a display element driving device and an organic EL display panel according to one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a variable constant voltage power supply circuit.

FIG. 3 is a timing chart showing the operation timing of each unit.

FIG. 4 is a diagram showing an anode line, a cathode line, and display dots.

FIG. 5 is a block diagram showing a display element driving device and an organic EL display panel according to a modified example.

FIG. 6 is a diagram illustrating a conventional display element driving device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic EL display panel 2 Anode line 3 Cathode line 4 Column driver 5 Row driver 11 Variable constant voltage power supply circuit 12 Control part 15 Display dot 17 Current detection circuit 18 Temperature detection element

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takayuki Tomita 1-7-10 Kikuzumi, Minami-ku, Nagoya-shi, Aichi F-term in Harness Research Institute, Ltd. (Reference) 3K007 AB00 AB02 AB17 BA06 CA01 CB01 DA00 DB03 EB00 FA01 GA00 5C080 AA06 BB05 DD05 EE29 FF12 JJ02 JJ03 JJ04

Claims (3)

[Claims] A plurality of thin film-formed transparent electrode lines are arranged in parallel, and a plurality of non-transparent electrode lines are arranged in parallel so as to intersect each of the transparent electrode lines. What is claimed is: 1. A display element driving device for performing a duty drive on an organic EL display panel having a dot matrix structure in which intersections with electrode lines are arranged in a matrix as display dots, wherein each switching element of a predetermined non-transparent electrode driver is used. While turning on in division and sequentially switching the non-transparent electrode line,
In synchronization with switching of each switching element of the non-transparent electrode driver, each switching element of a predetermined transparent electrode driver is selectively turned on / off in accordance with display contents to select the transparent electrode line, and each display dot is displayed. Wherein the transparent electrode driver is connected to one end of the transparent electrode line, and the display is performed through the transparent electrode driver and the transparent electrode line. A variable constant voltage power supply circuit for applying a drive voltage to the dots, while switching on the switching elements of the non-transparent electrode driver in a time-division manner and sequentially switching the non-transparent electrode lines,
In synchronization with switching of each switching element of the non-transparent electrode driver, each switching element of a predetermined transparent electrode driver is selectively turned on / off in accordance with display contents to select the transparent electrode line and time division. The variable constant voltage power supply circuit so as to change the drive voltage in proportion to a distance from an intersection of the non-transparent electrode line and the transparent electrode line, which are sequentially turned on, to the one end of the transparent electrode line. And a control unit for controlling the display device. 2. The display element driving device according to claim 1, further comprising a current detection circuit that measures a driving current output from the variable constant voltage power supply circuit, wherein the control unit is configured to control the current detection circuit. Wherein the variable constant-voltage power supply circuit is controlled based on a result of the current detection in the step (a) to stabilize the drive current. 3. The display element driving device according to claim 1, further comprising a temperature detecting element for detecting a temperature of the organic EL display panel, wherein the control unit is configured to control the organic EL display panel. A display element driving device configured to determine an initial level of the driving voltage based on a result of temperature detection by the temperature detecting element at the start of application of the driving voltage to the display element.